VB4-845 is a recombinantly expressed therapeutic protein consisting of a monoclonal antibody specific for the cell surface protein EpCAM linked to a truncated form of pseudomonas exotoxin ((Zangemeister-Wittke et al., 2006) WO04/096271A1, (Zangemeister-Wittke and Di Paolo, 2006) WO06/1635A2). VB4-845 is currently being produced using an E-coli based recombinant protein expression system.
During recombinant protein production in a heterologous system, improper folding of the nascent protein is often the cause of decreased yield of functional protein. Different approaches have been taken to improve folding and expression, including the use of chaperons, changes to the fermentation conditions to affect rate of production and various forms of re-engineering of the expression vector (Vasseur-Godbillon et al., 2006; Endo et al., 2006; Xu et al., 2005; Makrides, 1996; Baneyx et al., 1991).